Variable frequency cyclotron



Nov. 10, 1953 Filed April 27, 1951 W. W. SALISBURY VARIABLE FREQUENCYCYCLOTRON BIA 5 2 Sheets-Sheet l INVENTOR BYWmzb W SAuSBIIRY Y Nov. 10,1953 w. w. SALISBURY 2,659,000

VARIABLE FREQUENCY CYCLOTRON Filed April 27, 1951 2 Sheets-Sheet 2 1 VEN TOR.

To ac BY Wurnrlo W Salsa/RY BIAS 34' A TTORNEY Patented Nov. 10, 1953UNITED STATES PATENT OFFICE VARIABLE FREQUENCY CYCLOTRON Winfield W.Salisbury, Cedar Rapids, Iowa, as-

signor'to Collins Radio Company, Cedar Rapids, Iowa, a corporation ofIowa Application April 27, 1951 Serial No. 223,327

6 Claims. 1

This invention relates to means for controlling the frequency of asynchro-cyclotron with a frequency "modulated oscillator which suppliesan input to the dee chamber.

Synchro-cyclotrons or frequency modulated 'cyclotrons may be controlledby varying the capacitance of the dee system with a rotating condenserdriven by a motor. If the dee system is de-tuned, for any reason, thepower developed in the cyclotron falls appreciably and it is an objectof this invention to provide a frequency modulated oscillator which issynchronizedwith the tuning condenser and which feeds an input into thedee chamber to stabilize the cyclotron. This apparatus might be thoughtof as providing a feedback voltage to the cyclotron to thus stabilizethe resulting operating frequency.

It is an object of this invention, therefore, to provide a synchronizedfeedback frequency modulated oscillator which furnishes an input to thedee chamber'of the cyclotron.

Another object of this invention is to provide a stabilizing input tothe cyclotron derived from a replica condenser mounted on the maincondenser tuning shaft. The replica condenser controls the frequencymodulated oscillator which supplies the feedback.

Still another object of this invention is to provide a frequencymodulated cyclotron which has a feedback system comprising a frequencymodulated oscillator.

It is a feature of this invention to provide synchronizing means in afrequency modulated cyclotron which in controlled by a rotatingcondenser coupled to the dee system and which has a replica of thetuning condensers mounted on the driven shaft. The replica condenser isexcited by a constant frequency oscillator to derive an output voltageproportional to the variation in capacitance :of the replica condenser.The output of the replica condenser is rectified, and furnished to afrequency modulated oscillator which has the characteristic that itsfrequency is controlled by the direct current signal supplied to it. Theoutput of the frequency modulated oscillator is fed into the dee chamberas a feedback to obtain frequency stabilization.

Further objects, features, and advantages of this invention will becomeapparent from the following description and claims when read in view ofthe drawings, in which;

Figure 1 illustrates a frequency modulated cyclotron with thesynchronizing system of this invention installed therein; and,

Figure 2 is a sectional view taken on line 2--2 of Figure .1;

Figure 3 is a side view of the dee chamber illustrating the replicacondenser of this invention;

Figure 4 illustrates a phase shift oscillator;

Figure 5 illustrates a means of varying resistance with a direct currentpotential; and,

Figure 6 is a frequency shifting oscillator which embodies theprinciples of the circuits of Figures 4 and 5.

Synchro-cyclotrons are known to those skilled in the art and for a moredetailed description reference may be made to the Physical Review,volume 68, pages 143-145 (1945.) and Advances of Electronics, volume 1,pages 300-306, M. Stanley Livingston, published 1948 by Academic Pressof New York.

Figure 1 illustrates :a synchro-cyclotron, designated generally as 1-0.,which is formed with a cover H in which is mounted a dee l2. The dee isformed with a pair of stems I 3 and H which are received in projectionsl6 and -l 1, respectively, formed in the cover I1 and are electricallyconnected to them.

Mounted on the rear of the dee 1-2 are a plurality of stator condenserplates 18., as best shown .in Figure 2. The cover wall H has anextension l9 which extends over the plates I8. .A plurality of secondstator plates 21 are attached to the inside wall of extension i9 and aregenerally semi-circular in shape.

Rotor condenser plates 22 are mounted on a shaft 23 which is supportedin suitable bearings in the extension l9. The rotor plates 22 are formedwith projections 24 and it may be seen in Figure 1 that the statorplates 18 and 21,, and rotor plates 22 intermesh so that the rotor mayturn without engaging the stator plates.

The extension 19 is a part of the wall 1 l which is grounded and thusthe rotation of rotor 22 varies the capacitance to ground of the dee 12.The dee is grounded at the projections i3 and [4 but one-half wavelength exists between these points so that an anti-nodal point is formedwhere the stators I8 are connected to the dee l 2.

The shaft 23 extends out of the cover H and is connected at one end to amotor 26. The opposite end is mounted in a bearing 21. A rotor plate 28is mounted between the bearing 2'! and the wall it. The rotor plate 28has the same shape as the rotor plates 22. A pair of stator plates 29and 3-1 are mounted adjacent the rotor plate 28. The stator plates 29and 3| are generally U-shaped and their active portions that extendparallel to the rotor plate .28 are of the same general shape asthestator plates I 8 and 2|, respectively.

The small stator plate 31 receives an electrical input from anoscillator 32 which oscillates at a fixed frequency. The large statorplate 29 is connected to a rectifier 33 and the output of the rectifier33 is proportional to the position of the shaft 23. The oscillator 32might oscillate at 100 kilccycles, for example, and the output of therectifier 33 will produce a direct current output proportional to theshaft position.

A direct current biasing means 34 receives the output of rectifier 33 toadd an adjustable direct current voltage. The output of rectifier 33 issupplied to a frequency modulated oscillator 36 which will be describedin detail later. The oscillater 38 has the characteristic that itsfrequency may be controlled by the amplitude of a direct currentpotential. The output of the oscillator 35 is fed to an amplifier 31which increases its amplitude and couples it to the dee throu h a lead38 terminating in a coupling loop 39 within the stem I 3 of the dee.

The invention as described therefore utilizes a replica of the tuningcondenser to obtain a. direct current voltage to control the frequencyof a direct current controlled oscillator whose output is fed back intothe dee chamber.

In that the tuning condenser comprising the rotor plates 22 and statorplates l8 and 2i provide the frequency variation in the resonant deesystem, the output of the oscillator 35 will be the same as the desiredoperating frequency.

Uncontrollable factors within the dee chamber, however, sometimesprevent the frequency within the dee chamber from remaining constant andthe oscillator 36 provides a feedback which will stabilize theoscillator system of the cyclotron to prevent it from operating atspurious frequencies.

Attempts have been made to provide a stabilizing feedback for acyclotron of this nature by coupling a small amount of energy from thecyclotron, amplifying it, and feeding it back into the chamber as astabilizing component. This procedure, however, has not been whollysuccessful for the reason that the feedback signal is not independent ofthe undesirable effects present in the cyclotron chamber. Applicantsreplica condenser comprising the rotor 28 and the stators 29 and 3| isindependent of the resonant conditions within the dee chamber and thus afeedback signal controlled in frequency by this condenser will beindependent of the conditions existing within the dee chamber.

The frequency modulated oscillator 36 is shown in detail in Figure 6. Itis a phase shift oscillator and basically is derived from the oscillatorillus trated in Figure 4. The oscillator 36 must be capable of varyingits frequency over broad limits very rapidly. For example, applicant hasbuilt an oscillator variable from 18 to 25 megacycles during anoperating cycle of the cyclotron.

The basic phase shift oscillator, as shown in Figure 4, comprises a tubeV1 which is a broad band amplifier. The output of the plate of theamplifier V1 is connected to a phase shift circuit comprising thecondensers C and the resistors R. The output of the phase shift circuitis fed to the control grid 41 of the broad band amplifier V1 and thecircuit will oscillate if the loss through the phase shift circuit isless than the gain of the tube. The frequency of oscillation isdetermined by the phase shift of the phase shift network. The signalsupplied to the grid 6! must be 180 degrees (or some odd multiplethereof) out of phase with the plate signal for oscillation to occur.Thus, if the phase shift through t phase shifting circuit is varied theresonant frequency will change.

Suppose. for example, that in the phase shift circuit of Figure 4 thevalues of C are equal and the values of R are equal. For oscillation tooccur the phase shift across the three sections must be 180 degrees, or60 degrees across each RC section. By varying the resistors R, orcapacitors C the resonant frequency will change. For a more detaileddescription of the phase shift frequency modulation oscillator,reference may be made to page 1328 of volume 2'7 of the Proceedings ofthe Institute of Radio Engineers.

Figure 5 illustrates a circuit for varying the phase shift in an RCcircuit with a direct current voltage. The condenser C1 is connected tothe plate 42 of a tube V2 which has its cathode 43 connected to groundand a second condenser Cy. is connected to the condenser C1. A pair ofresistors R1 and R2 are connected between 3-]- and opposite sides of thecondenser C2. A by-pass condenser C3 is connected between 3+ and ground.

The condensers C1, C2, resistors R1 and R2, with a tube V2 comprise aphase shift circuit. The tube V2 has a plate resistance depending uponthe bias placed on grid 44, and thus tube V: is analogous to thevariable resistors illustrated in Figure 4. If the bias supplied to grid44 is varied, the plate resistance of the tube will be varied and thephase shift across circuit of Figure 5 will change.

It is seen that the circuit of Figure 5 makes it possible to control thephase shift of a circuit with a direct current voltage applied to thegrid 44. By utilizing this principle applicant has designed the circuitof Figure 6.

The circuit of Figure 6 might be thought of as four phase shiftoscillators of the type shown in Figure 4 connected in series so thatthe gain of each amplifier is additive and the output is thereforegreater. Instead of using the phase shift circuit shown in Figure 4applicant has used a phase shift circuit such as shown in Figure 5 tocontrol the frequency of the four oscillators.

The tubes V3, V4. V5 and V6 are the broad band amplifier tubes whichcorrespond to tube V1 in Figure 4. The tubes V7, V5, V9, and Vmcorrespond to the tube V2 in the phase shift circuit of Figure 5. If thetube V3 is to be used in a phase shift oscillator, it is known that foroscillation to occur, the feedback received on grid 46 must be 180degrees (or some odd multiple thereof) out of phase with the platevoltage on plate 41.

Assume that the phase shift between plate 4'! and the grid 48 of tube V4is degrees. The phase shift between plate 49 and the grid 48 of tube V4will be degrees and the phase shift between the plate 49 and the plate41 will be equal to 180 degrees plus 90 or 2'70 degrees. Assume onceagain that the phase shift between the plate 49 and the control grid 5|of tube V5 is 90 degrees. The phase shift between the grid 51 and theplate 52 will be 180 degrees so that the phase shift between the plate52 and the plate 41 will be 540 degrees.

If the phase shift between the plate 52 and the grid 53 of tube V6 isassumed to be 90 degrees, then the plate 54 of tube V6 will be 810degrees out of phase with the plate 41 of tube V3. If the phase shiftbetween the plate 54 and the grid 46 is 90 degrees then the total phaseshift between the grid 46 and the plate 4'! of tube Va will be- 900degrees; which is equal to (5x180) and thus, oscillation can occur.

The output ofany of the tubes V3, V4, V5, or V6 may-be used asthe-oscillatorsoutput. A lead 55 isconneeted to plate 49 of tube V4 andisconnected to the amplifier 31'.

The phase shift tubes V'z, V8, V0, and V have their control, grids 5T,58, 59 and 6|, respectively, connectedtogether and to terminal 62* whichis connected to the direct current. bias 34. Thus, the bias applied toterminal 62 varies the plate resistanceof the tubes V7 through V10,andresults ina varying phase shift through the phase shift circuits. Itis seen that the circuitry between the amplifiers V3 and V4. correspondsto the phase shift circuitry of Figure 5.. Each of the phase shiftcircuits between amplifiers are the same.

In that each phase shift circuit has only a 90 degree phase shift ratherthan a 180 degree phase shift, less loss will be encountered than in thecircuit of Figure 4. It is well known that in an RC phase shift circuit,the greater the phase shift, the greater the attenuation.

It is to be understood, of course, that the ring oscillator of Figure 6may be modified to add more or less phase shift oscillator segments. Theinput to each amplifier grid must remain 180 degrees (or some oddmultiple) out of phase with the plate voltage.

It is seen that this invention provides a stabilizing feedback systemfor a synchro-cyclotron which has a novel ring oscillator.

Although the invention has been described with respect to a preferredembodiment thereof, it is not to be so limited as changes andmodifications may be made therein which are within the full intendedscope as defined by the appended claims.

I claim:

1. Means for controllin the frequency of a synchro cyclotron comprising,a cover member, a dee system mounted within said cover member, a rotorshaft rotatably supported by said cover member, first rotor condenserplates mounted on said rotor shaft within said cover member, firststator condenser plates mounted on the dee system, second statorcondenser plates connected to the cover member, a driving means mountedto the rotor shaft externally of the cover member, third statorcondenser plates of the same general shape as the second statorcondenser plates mounted adjacent said rotor shaft, second rotorcondenser plates mounted on the rotor shaft adjacent the third statorcondenser plates, fourth stator condenser plates mounted adjacent thesecond rotor condenser plates and the third stator condenser plates, anoscillator connected to the third stator condenser plates, a frequencymodulation oscillator with its frequency controlled by direct currentbias from the rectifier, and a feedback loop within the cover memberreceiving an input from the frequency modulation oscillator to coupleenergy to th dee system.

2. Means for controlling the frequency of a frequency modulationcyclotron comprising, a

driving means, a rotor shaft rotatably supported by the cyclotron, firstrotor condenser plates mounted on said rotor shaft, a dee mounted withinsaid cyclotron, first stator condenser plates mounted on the dee, secondrotor condenser plates and second and third stator condenser plates,said second rotor condenser plates mounted on said rotor shaftexternally of said cyclotron, said second and third stator condenserplates mounted adjacent the second rotor con- 6 denser plates, a firstfrequency oscillator'supplying aninput to the second stator condenserplates, a rectifier receiving an input from the third statorccndenser'plates, a frequency modulation oscillator with its frequencycontrollable by 'directcurrent received from said rectifier, andanenergycoupling means connected to the output. of the frequencymodulation oscillator to couple it into the dee system of the cyclotron.

3'. Means for controlling the frequency of a synchro cyclotroncomprising, a driving means, a rotor shaft rotatably supported by saidcyclotron and connected to said driving means, first rotor condenserplates mounted on the rotor shaft Within the cyclotron, first and secondstator condenser plates mounted in the cyclotron adjacent the firstrotor condenser plates, second rotor condenser plates mounted on therotor shaft, third and fourth stator condenser plates mounted adjacentthe second rotor condenser plates, a first frequency oscillatorconnected to and supplying an input to the third stator condenserplates, at rectifier connected to the fourth stator condenser plates, afrequency modulation oscillator receiving an input from said rectifierand varying the frequency of its output in response thereto, and energycoupling means receiving the output of the frequency modulationoscillator and coupling it into the dee system of the cyclotron.

4. Means for controlling the frequency excursions of a synchro cyclotroncomprising, a cover member, a dee system mounted within the covermember, a rotor shaft rotatably supported by the cover member, a drivingmeans connected to the rotor shaft, first rotor condenser plates mountedon the rotor shaft within the cover member, second rotor condenserplates mounted on the motor shaft externally of the cover member and ofthe same general shape as the first rotor condenser plates, first andsecond stator condenser plates mounted within said cyclotron adjacentsaid first rotor condenser plates, third and fourth stator condenserplates mounted externally of the cyclotron adjacent the rotor condenserplates, a first frequency oscillator connected to the third statorcondenser plates, a rectifier receiving an input from the fourth statorcondenser plates, a direct current biasing means receiving the output ofthe rectifier and producing a varying direct current output, afrequencymodulation oscillator with its frequency controlled by theoutput of the direct current biasing means, and energy coupling meansreceiving the output of the frequency modulation oscillator to couple itinto the dee system of the cy clotron.

5. Apparatus according to claim 4 wherein said frequency modulationoscillator comprises, a plurality of phase shift oscillators with theiroutputs connected in series and the phase shift portions of each phaseshift oscillator having tubes whose plate resistance may be varied bythe direct current bias on their grids, and the grids of er member,second rotor condenser plates mounted on the rotor shaft externally ofthe cover memher and having the same general shape as the first rotorcondenser plates, third stator condenser plates supported adjacent thesecond rotor condenser plates, fourth stator condenser plates mountedadjacent the second rotor condenser plates, a fixed frequency oscillatorconnected to the third stator condenser plates, a reotifier connected tothe fourth stator condenser plates, direct current biasing meansconnected to the rectifier, a frequency modulation oscillator connectedto the direct current biasing means, energy coupling means connected tothe frequency modulation oscillator and coupled to the dee system of thecyclotron, said frequency modulation oscillator comprising a ringoscillator with a plurality of broad band amplifier tubes connected withphase shift circuits between them, and the phase shift circuits havingphase shift tubes which receive the input from the direct current biasinmeans on their control grid to vary their plate to cathod resistance.

WINFIELD W. SALISBURY.

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